Reteachable non-contact switching circuit

ABSTRACT

A method for reteaching a switching circuit is provided. The method includes presenting a target within a sensing range of a sensor of the switching circuit for a pre-determined duration and acquiring an identification code of the target via the sensor. The method also includes comparing the acquired identification code with all stored identification codes of other targets previously used by the switching circuit as a basis for switching and reteaching the switching circuit for switching based on the acquired identification code if the acquired identification code is different from all stored identification codes previously used by the switching circuit as a basis for switching.

BACKGROUND

The invention relates generally to switching devices, such as formachine guarding in industrial applications, and particularly toreteachable switching circuits.

Switching devices are known and are in use for controlling devices intechnical installations. Typically, such switching devices areconfigured to facilitate partial or complete shutdown of electricallydriven machines/devices of the technical installation to limit access tothe technical installation, at least during certain periods ofoperation.

One type of switching device is a door switch that includes anactuator-sensor combination for detecting an open state of an accessdoor of the technical installation. Typically, the actuator is codedwith a unique identification code that is utilized by the sensor todetect the open state of the access door.

In general, it is desirable to provide switching devices that can beretaught for new actuators in the event that an existing actuator isdamaged in the field. However, this may result in maintenance personnelby-passing the switch by using spare actuators taped or otherwiseaffixed to or near the face of the switch and reteaching the switch forthe actuator mounted on the access door. Further, reteaching of theswitch for a new actuator may require disruptive steps such as cyclingpower thereby resulting in substantial downtime of machines/devices ofthe technical installation.

Accordingly, it would be desirable to provide a robust and secureswitching device that can be easily retaught for new actuators withoutrequiring complex or disruptive steps while providing security againstreteaching of the switching device for previously used/damagedactuators.

BRIEF DESCRIPTION

Briefly, according to one embodiment of the present invention, a methodfor reteaching a switching circuit is provided. The method includespresenting a target within a sensing range of a sensor of the switchingcircuit for a pre-determined duration and acquiring an identificationcode of the target via the sensor. The method also includes comparingthe acquired identification code with all stored identification codes ofother targets previously used by the switching circuit as a basis forswitching and reteaching the switching circuit for switching based onthe acquired identification code if the acquired identification code isdifferent from all stored identification codes previously used by theswitching circuit as a basis for switching.

In accordance with another aspect, a method of reteaching a switchingcircuit is provided. The method includes presenting a target within asensing range of a sensor of the switching circuit for a pre-determinedduration and acquiring an identification code of the target via thesensor. The method also includes comparing an acquired identificationcode with a stored identification code of a target previously used bythe switching circuit as a basis for switching and reteaching theswitching circuit for switching based on the acquired identificationcode if the acquired identification code is different from the storedidentification code, wherein the acquiring, comparing and reteachingsteps are performed without operator manipulation of the switchingcircuit.

In accordance with another aspect, a reteachable switching circuit isprovided. The reteachable circuit includes a non-contact sensor and atarget movable into and out of a sensing range of the sensor. Thereteachable circuit also includes a memory configured to store aplurality of identification codes of other targets previously used bythe switching circuit as a basis for switching and a processorconfigured to reprogram the switching circuit for the detected target ifan acquired identification code of the target is different from allstored identification codes previously used by the switching circuit asa basis for switching.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates a technical installation such as an electricalmachine within a controlled access environment in accordance withaspects of the present invention;

FIG. 2 illustrates another exemplary embodiment of an installation ofFIG. 1 in accordance with aspects of the present invention;

FIG. 3 illustrates another exemplary embodiment of the installation ofFIG. 1 in accordance with aspects of the present invention;

FIG. 4 illustrates an exemplary configuration of the switching circuitsemployed in the installations of FIGS. 1, 2 and 3, respectively, inaccordance with aspects of the present invention;

FIG. 5 illustrates an exemplary process of reteaching the switchingcircuits of FIG. 4 in accordance with aspects of the present invention;

FIG. 6 illustrates an exemplary process of locking the switchingcircuits of FIG. 4 against learning of identification codes of newtargets in accordance with aspects of the present invention; and

FIG. 7 illustrates exemplary process steps of identifying a valid targetfor reteaching the switching circuit of FIG. 4 in accordance withaspects of the present invention.

DETAILED DESCRIPTION

As discussed in detail below, embodiments of the present techniquefunction to provide a method for reteaching a switching circuit such asnon-contact switching circuits employed for machine guarding inindustrial applications. In particular, the present technique provides aswitching circuit that can be re-taught for a new target without anyoperator manipulation of the switching circuit. Further, the presenttechnique also provides a locking mechanism for the switching circuitthat enables locking of the switching circuit against learning a newtarget prior to reaching an allowed number of reteaching attempts.

References in the specification to “one embodiment”, “an embodiment”,“an exemplary embodiment”, indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

Turning now to drawings and referring first to FIG. 1, a technicalinstallation such as an electrical machine 10 within a controlled accessenvironment 12 is illustrated. The machine 10 includes a power supply 14to power a plurality of switching circuits 16, 18 and 20 disposed onaccess doors 22, 24 and 26 respectively of the installation. In theillustrated embodiment, the power supply 14 includes a 24 volts DC powersupply. The switching circuits 16, 18 and 20 are configured to monitorposition of each of the access doors 22, 24 and 26 and to interruptoperation of the installation completely or partially to preventuncontrolled access to the installation when the doors 22, 24 and 26 areopen.

In the illustrated embodiment, each of the switching circuits 16, 18 and20 includes a non-contact sensor disposed on a stationary component suchas a frame of each of the access doors 22, 24 and 26 and a target suchas an actuator disposed on a movable component such as on surface ofeach of the access doors 22, 24 and 26. In a closed state of the accessdoors 22, 24 and 26, the actuator is located within the sensing range ofthe sensor, which causes an enable signal to be generated.Alternatively, in an open state of any of the access doors 22, 24 and26, the actuator is removed from the sensing range of the sensor, whichgenerates a switching signal for interrupting operation of one or morecomponents of the installation completely or partially through one ormore devices, such as represented by reference numeral 28.

In certain embodiments, the machine 10 includes output signal switchingdevices (OSSDs) that are configured to switch DC powered devices, suchas contactors and control relays of the installation. In one exemplaryembodiment, the OSSDs include PNP type transistors with short circuitprotection, overload protection and crossfault detection.

In this exemplary embodiment, the switching circuits 16, 18 and 20utilize radio frequency identification for coding of the actuator andinduction for sensing by the sensor. The teaching of such switchingcircuits 16, 18 and 20 will be described in detail below with referenceto FIGS. 4-6. In certain embodiments, the devices 28 include machineactuators or logic devices such as monitoring relays configured tointerrupt one or more components of the installation. The monitoringrelays may include two or more guided relays with additional circuitryto ensure performance of the access limiting function.

FIG. 2 illustrates another exemplary embodiment 40 of an installation 10of FIG. 1. As illustrated, the installation 40 includes switchingcircuits 16, 18 and 20 for monitoring a position of each of the accessdoors 22, 24 and 26. In this embodiment, the installation 10 includes acontroller 42 configured to receive switching signals from the switchingdevices 16, 18 and 20 and to generate output signals for the devices 28.In certain embodiments, the controller 42 includes a programmable logiccontroller (PLC) with solid-state outputs. In operation, the devices 28may be operated by the controller 42 in response to signals from theswitching circuits 16, 18 and 20. Thus, the devices 28 may shut down orinterrupt operation of certain devices of the installation 40 if theswitching circuits 16, 18 and 20 detect any of the access doors 22, 24and 26 in an open state.

FIG. 3 illustrates another exemplary embodiment 50 of the installation10 of FIG. 1. In this embodiment, the installation 50 includes a network52 to receive switching signals from the switching circuits 16, 18 and20 and to control operation of the devices 28. In certain embodiments,the installation 50 includes a remote controller 54 communicativelycoupled to the network 52 to analyze the switching signals and tocontrol the operation of the devices 28 to shut down or interruptoperation of certain equipment of the installation 50 based upon suchswitching signals. As will be appreciated by one skilled in the art thenetwork 52 may include components such as network cables, networkinterface cards, routers and bridges to communicate with the devices 28and the controller 54.

As described above, each of the switching circuits 16, 18 and 20includes the sensor and the target that has a unique identificationcode. Each of the switching circuits 16, 18 and 20 is configured to beretaught a new target without operator manipulation of the switchingcircuits 16, 18 and 20. Furthermore, an operator can lock each of theswitching circuits 16, 18 and 20 against further reteaching of any othertargets as will be described below.

FIG. 4 illustrates an exemplary configuration 60 of the switchingcircuits 16, 18 and 20 employed in the installations 10, 40 and 50 ofFIGS. 1, 2 and 3 respectively. Each of the switching circuits 16, 18 and20 includes a non-contact sensor 62 and a target 64 movable into and outof a sensing range of the sensor 62. In one embodiment, the sensingrange of the sensor 62 is between about 10 mm and about 25 mm. In theillustrated embodiment, the sensor 62 is disposed on a stationarycomponent such as frame of the access door 22 (see FIG. 1). Further, thetarget 64 includes an actuator disposed on a movable component such asthe access door 22.

The actuator 64 is coded with an identification code using radiofrequency identification. In one exemplary embodiment, theidentification code includes a 16-bit word. In operation, the sensor 62generates a radio frequency field, generally represented by referencenumeral 66, at frequency of about 125 kHz and the target 64 is a passiveresonant circuit that responds to excitation by the radio frequencyfield. Moreover, each of the switching circuits 16, 18 and 20 includescomponents 68 for reteaching the switching circuits 16, 18 and 20.

In particular, each of the switching circuits 16, 18 and 20 includes amemory 70 configured to store a plurality of identification codes ofother targets previously used by the switching circuits 16, 18 and 20respectively as a basis for switching. The memory 70 may include harddisk drives, optical drives, tape drives, random access memory (RAM),read-only memory (ROM), programmable read-only memory (PROM), redundantarrays of independent disks (RAID), flash memory, magneto-opticalmemory, holographic memory, bubble memory, magnetic drum, memory stick,Mylar® tape, smartdisk, thin film memory, zip drive, and so forth.

Further, each of the switching circuits 16, 18 and 20 includes aprocessor 72 configured to reteach the switching circuits 16, 18 and 20for the target if an acquired identification of the target is differentfrom all stored identification codes previously used by the switchingcircuits 16, 18 and 20 respectively as a basis for switching. Inaddition, each of the switching circuits 16, 18 and 20 includes adisplay 74 to display warning messages if the identification code of thetarget is identical to any stored identification code previously used bythe switching circuits 16, 18 and 20 respectively as the basis forswitching.

It should be noted that the present invention is not limited to anyparticular processor for performing the processing tasks of theinvention. The term “processor,” as that term is used herein, isintended to denote any machine capable of performing the calculations,or computations, necessary to perform the tasks of the invention. Theterm “processor” is intended to denote any machine that is capable ofaccepting a structured input and of processing the input in accordancewith prescribed rules to produce an output. It should also be noted thatthe phrase “configured to” as used herein means that the processor isequipped with a combination of hardware and software for performing thetasks of the invention, as will be understood by those skilled in theart.

In certain embodiments, each of the switching circuits 16, 18 and 20 mayinclude a buffer memory (not shown) configured to store sensing datacorresponding to the target 64 within a pre-determined duration tovalidate the acquired identification code of the target 64. In oneexemplary embodiment, the pre-determined duration is about 15 secs. Itshould be noted that the processor 72 is configured to reprogram theswitching circuit such as 16 without operator manipulation of theswitching circuit 16. Advantageously, the reteaching of the switchingcircuits 16, 18 and 20 can be performed without power cycling andwithout any manipulation of jumper connections of the switching circuits16, 18 and 20.

In certain embodiments, the processor 72 is configured to reprogram theswitching circuit such as 16 based upon the identification code of thetarget and to lock the switching circuit 16 against further reteachingbased upon other identification codes of any other targets prior toreaching an allowed number of reteaching attempts. In one exemplaryembodiment, the allowed number of reteaching attempts is 8. However, agreater or lesser number may be assigned for the allowed number ofreteaching attempts. It should be noted that an operator of the systemmay lock the switching circuit 16 either immediately after commissioningor after any subsequent successful learn of the switching circuit 16 fora target 64.

In operation, the target 64 is presented within the sensing range of thesensor 62 for a pre-determined duration and the identification code ofthe target 64 is acquired via the sensor 62. In this exemplaryembodiment, the pre-determined duration is about 15 seconds. Further,the acquired identification code is stored in the memory 70. Theswitching circuit 16 may be subsequently locked against learningidentification codes of any other target prior to reaching the allowednumber of reteaching attempts.

In this exemplary embodiment, each of the switching circuits 16, 18 and20 includes one or more light emitting diodes (LEDs), such asrepresented by reference numeral 76 for identifying location of faultsin the installation 10. For example, a green light emitted by the LED 76of the switching circuit 16 indicates that the target 64 is within thesensing range of the sensor 62 and the switching circuit 16 isfunctioning properly. Similarly, a flashing red light emitted by the LED76 of the switching circuit 18 indicates that the switching circuit 18has a fault and is not functioning properly. Further, a red lightemitted by the LED 76 of the switching circuit 20 indicates that thetarget 64 is outside the sensing range of sensor 62. Thus, based uponindications from the LED 76 of the various switching circuits 16, 18 and20 any faults within the installation 10 may be detected and corrected.

FIG. 5 illustrates an exemplary process 90 of reteaching the switchingcircuits 16, 18 and 20 of FIG. 4. At block 92, the process is initiatedand the power is supplied to the switching circuit. Further, a target ispresented within the sensing range of the sensor of the switchingcircuit. At block 94, the presence of the new target is detected and asolid red light is displayed by the LED of the switching device toindicate the absence of a learned target. In the illustrated embodiment,the target is presented in the sensing range for a pre-determinedduration. In one exemplary embodiment, the pre-determined duration isabout 15 secs. At block 98, it is validated if the target is present forthe pre-determined duration.

Further, it is verified if the target is an acceptable actuator for theswitching circuit (block 100). If the target is not an acceptableactuator then the switching device displays an error code using the LEDof the switching device, as represented by block 102. In this exemplaryembodiment, power cycling of the switching device is required for theswitching device for an unacceptable target, as represented by block104.

Alternatively, once an acceptable target is detected, then the switchingdevice proceeds with reteaching of the switching device for the targetby acquiring the identification code of the target via the sensor. Atblock 106, a timed loop with a pre-determined duration is initiated. Inthis exemplary embodiment, the timed loop has duration of about 15seconds. During the timed loop, green and red light may be displayedalternately by the LED of the switching device (block 108). The timedloop is completed after the pre-determined duration, as represented byblock 110. At block 112, the switching device validates if the targetwas present continuously during the timed loop. If the target was notpresent within the sensing range of the sensor for the entire durationof the timed loop, then an error code is displayed by the switchingdevice (block 114).

At block 116, the sensed data during the timed loop is compared tovalidate the acquired identification code of the target and powercycling of the switching device is performed if the acquired code isinvalid (block 104). In this exemplary embodiment, the identificationcode of the target is repeatedly sensed within the timed loop and iscompared to validate the acquired code. At block 118, the switchingdevice verifies if the current reteaching attempt is less than anallowed number of reteaching attempts. If the current reteaching attemptis greater than the allowed number of reteaching attempts, then an errorcode sequence is initiated, requiring power cycling.

Once the acquired identification code of the target is validated, it iscompared with all stored identification codes of other targetspreviously used by the switching circuit as a basis for switching.Further, the switching circuit is retaught based on the acquiredidentification code only if the acquired code is different from allstored identification codes of other targets previously used by theswitching circuit as a basis for switching. The acquired identificationcode is then stored for operating the switching circuit.

Further, the switching circuit may be locked against learningidentification codes of any other target prior to reaching an allowednumber of reteaching attempts, as illustrated by exemplary process 120of FIG. 6. At block 122, a timed loop for a pre-determined period for avalid target is initiated. In this exemplary embodiment, duration of thepre-determined period is about 15 secs. At block 124, number ofavailable reteaching attempts is displayed by the LED of the switchingdevice. Further, it is verified if the target is moved outside thesensing range of the sensor and is represented within the sensing rangewithin the pre-determined period (block 126).

In this exemplary embodiment, opening and closing of a movable componentsuch as an access door where the target is mounted is monitored toverify if the target is moved outside and is re-presented within thesensing range. In one exemplary embodiment, if the opening and closingof the movable component is performed at least once during thepre-determined period, then the locking of the switching device isinitiated. At block 128, the timed loop is ended and a green light isdisplayed by the LED of the switching device to indicate the completionof the timed loop (block 130). At block 132, the switching device islocked against learning identification codes of any other target.Further, the switching device is operated with the acquiredidentification code of the target (block 134).

If the opening and closing of the movable component is not performed atleast once during the pre-determined period and the timed loop iscompleted, as represented by blocks 136 and 138, then the learningability of the switching device is in the unlocked state (block 140).Thus, the switching device is open for learning identification codes ofother target presented within the sensing range of the sensor of theswitching device. Again, the switching device is operated with theacquired identification code of the target (block 142).

FIG. 7 illustrates exemplary process steps 150 of identifying a validtarget for reteaching the switching circuit 16 of FIG. 4. At block 152,the identification code of the target is acquired using the sensor ofthe switching device. In this exemplary embodiment, the identificationcode includes a 16-bit word. In this embodiment, the sensor generates aradio frequency field at a frequency of about 125 kHz and the target isa passive resonant circuit that responds to the excitation by the radiofrequency field. At block 154, the acquired identification code iscompared with currently learned stored identification code used by theswitching circuit as a basis for switching. If the acquiredidentification code is identical to the currently stored code, then anew code is not learnt and the switch continues normal operation.

If the acquired identification code is different from the currentlystored identification code used by the switching circuit as a basis forswitching, then it is verified if the state change counter of theswitching device is equal to zero (block 156). The state change counterserves as a filter to ensure that not every new identification code isvalidated by the process. The state change counter is incremented if areading matches the previous. If three readings in a row match, thevalidation process is triggered. If the state change counter is equal tozero, then a buffer is set equal to the current data and the statechange counter is incremented (blocks 158 and 160). The sensor thenacquires the next data reading.

Alternately, if the state change counter is not equal to zero, then itis verified if the current sensed data is equal to the buffer (block162). If the current sensed data is not equal to the buffer, then thebuffer and the counters are initialized, as represented by block 164.The sensor then acquires the next reading of the target.

If the current sensed data is equal to the buffer, then the state changecounter is incremented and it is verified if the state change counter isequal to three (blocks 166 and 168). The state change counter serves asa filter to ensure that not every new identification code is validatedby the process. The state change counter is incremented if a readingmatches the previous. If three readings in a row match, the validationprocess is triggered. If the state change counter is not equal to three,then the sensor proceeds to acquire the next reading corresponding tothe target in the sensing range of the sensor.

Alternately, if the state change counter is equal to three, then a timerloop of pre-determined period is initiated (block 170). In one exemplaryembodiment, the pre-determined period of the timer loop is about 15seconds. At block 172, if the current sensed data is equal to the tempbuffer, then the data counter is incremented before the timer loop iscompleted, as represented by block 174.

At block 176, it is verified if the data counter is greater than orequal to a pre-determined threshold. In this embodiment, thepre-determined threshold is about 90%. If the data counter is less thanthe pre-determined threshold, then the output is set for no targetpresent in the sensing range of the sensor (block 178). Subsequently,all buffers and counters are initialized, as represented by block 180.Alternatively, if the data counter is greater than or equal to thepre-determined threshold, then the sensed data is stored in the memoryand the output is set for target present in the sensing range of thesensor (block 184). Again, all buffers and counters are initialized, asrepresented by block 180. Thus, once a valid target is detected, theswitching circuit may be reprogrammed for the corresponding target andthe identification code of the target is stored for operation of theswitching circuit.

As will be appreciated by those of ordinary skill in the art, theforegoing example, demonstrations, and process steps may be implementedby suitable code on a processor-based system, such as a general-purposeor special-purpose computer. It should also be noted that differentimplementations of the present technique may perform some or all of thesteps described herein in different orders or substantiallyconcurrently, that is, in parallel. Furthermore, the functions may beimplemented in a variety of programming languages, such as C++ or JAVA.Such code, as will be appreciated by those of ordinary skill in the art,may be stored or adapted for storage on one or more tangible, machinereadable media, such as on memory chips, local or remote hard disks,optical disks (that is, CD's or DVD's), or other media, which may beaccessed by a processor-based system to execute the stored code. Notethat the tangible media may comprise paper or another suitable mediumupon which the instructions are printed. For instance, the instructionscan be electronically captured via optical scanning of the paper orother medium, then compiled, interpreted or otherwise processed in asuitable manner if necessary, and then stored in a computer memory

The various aspects of the structures described hereinabove may be usedfor reteaching switching circuits for various machines. In theinstallations discussed above, the present techniques would be used tolimit access to a workspace, machine, or the like. Many otherapplications exist, however, for verifying position of a movablecomponent with respect to a stationary component (or the position of twomovable components with respect to one another) that may be the subjectof application of the presently claimed techniques. In particular, thetechnique may be employed for machines where multiple access doors arerequired to be monitored employed in industries such as materialhandling, packaging, life sciences and fiber and textiles, to name justa few. As described above, the technique utilizes a reteaching methodfor training the switching circuit for a target without operatormanipulation of the switching circuit. Thus, any machine with a damagedtarget can resume working with new targets in relatively lesser timewithout requiring complex or disruptive steps such as cycling power etc.

The technique described above also provides locking of the switchingcircuit against learning of codes of new targets prior to reaching anallowed number of reteaching attempts. Advantageously, the techniquefacilitates reteaching of the switching circuit for a new target in anevent where the target has been damaged in the field while preventingby-passing of the switch by using any spare targets taped to the face ofthe switch by the operator/maintenance personnel thereby providing arobust and secure switching device

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A method for reteaching a switching circuit, comprising: presenting atarget within a sensing range of a sensor of the switching circuit for apre-determined duration; acquiring an identification code of the targetvia the sensor; comparing the acquired identification code with allstored identification codes of other targets previously used by theswitching circuit as a basis for switching; and reteaching the switchingcircuit for switching based on the acquired identification code if theacquired identification code is different from all stored identificationcodes previously used by the switching circuit as a basis for switching.2. The method of claim 1, comprising: repeatedly sensing data within thepre-determined duration; and comparing the sensed data to validate theacquired identification code of the target.
 3. The method of claim 1,wherein reteaching the switching circuit comprises: validating thetarget presented within the sensing range of the sensor; and storing theacquired identification code for operating the switching circuit.
 4. Themethod of claim 1, wherein the sensor is disposed on a stationarycomponent and the target comprises an actuator disposed on a movablecomponent within the sensing range of the sensor.
 5. The method of claim1, wherein the pre-determined duration is about 15 seconds.
 6. Themethod of claim 1, comprising detecting the target within the sensingrange of the sensor through radio-frequency identification.
 7. Themethod of claim 1, further comprising rejecting the identification codeof the target if the acquired identification code is identical to astored identification code of a target previously used by the switchingcircuit as a basis for switching.
 8. The method of claim 7, furthercomprising displaying a warning message to a user if the acquiredidentification code is rejected.
 9. A method of reteaching a switchingcircuit, comprising: (a) presenting a target within a sensing range of asensor of the switching circuit for a pre-determined duration; (b)acquiring an identification code of the target via the sensor; (c)comparing an acquired identification code with a stored identificationcode of a target previously used by the switching circuit as a basis forswitching; and (d) reteaching the switching circuit for switching basedon the acquired identification code if the acquired identification codeis different from the stored identification code; wherein steps (b),(c), and (d) are performed without operator manipulation of theswitching circuit.
 10. The method of claim 9, wherein the operatormanipulation comprises power cycling of the switching circuit, andmanipulation of a jumper connection.
 11. The method of claim 9, furthercomprising: validating the target presented within the sensing range ofthe sensor; and storing the acquired identification code for operatingthe switch.
 12. A reteachable switching circuit, comprising: anon-contact sensor; a target movable into and out of a sensing range ofthe sensor; a memory configured to store a plurality of identificationcodes of other targets previously used by the switching circuit as abasis for switching; and a processor configured to reprogram theswitching circuit for the detected target if an acquired identificationcode of the target is different from all stored identification codespreviously used by the switching circuit as a basis for switching. 13.The reteachable switching circuit of claim 12, wherein sensor isdisposed on a stationary component and the target comprises an actuatordisposed on a movable component.
 14. The reteachable switching circuitof claim 12, wherein the identification code of the target comprises a16 bit word.
 15. The reteachable switching circuit of claim 12, furthercomprising a buffer memory configured to store sensing datacorresponding to the target within a pre-determined duration to validatethe acquired identification code of the target.
 16. The reteachableswitching circuit of claim 15, wherein the pre-determined duration isabout 15 seconds.
 17. The reteachable switching circuit of claim 12,wherein the processor is configured to reteach the switching circuitwithout operator manipulation of the switching circuit.
 18. Thereteachable switching circuit of claim 17, wherein the operatormanipulation comprises power cycling of the switching circuit, andmanipulation of a jumper connection.
 19. The reteachable switchingcircuit of claim 12, wherein the sensing range of the sensor is betweenabout 10 mm to about 25 mm.
 20. The reteachable switching circuit ofclaim 12, wherein the sensor generates a radio frequency field atapproximately 125 kHz, and the target is a passive resonant circuit thatresponds to excitation by the radio frequency field.